This invention relates to an ink jet printing process for improving the wet abrasion resistance of an ink jet image formed from an aqueous ink containing a cationic dye.
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant which is molecularly dispersed or solvated by a carrier medium. The carrier medium can be a liquid or a solid at room temperature. A commonly used carrier medium is water or a mixture of water and organic co-solvents. Each individual dye molecule is surrounded by molecules of the carrier medium. In dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor light-fastness. When water is used as the carrier medium, such inks also generally suffer from poor wet abrasion.
JP 10-219157 relates to an ink jet ink comprising an aqueous medium, a colorant and a very small amount of glutaraldehyde as a biocide.
There is a problem with using this ink, however, in that when it is printed on an image-recording element, the resultant image has poor wet abrasion resistance.
It is an object of this invention to provide an ink jet printing process for improving the wet abrasion resistance of an ink jet image formed from an aqueous ink containing a cationic dye. It is another object of this invention to provide an ink jet printing process wherein a hardener is applied to improve the wet abrasion resistance of the ink jet image. It is another object of the invention to provide an ink jet printing process where the laydown of the hardener applied can be precisely controlled independently of ink laydown and can be applied non-imagewise to the entire element.
These and other objects are achieved in accordance with the present invention which comprises an ink jet printing process for improving the wet abrasion resistance of an ink jet image comprising:
a) providing an ink jet recording element comprising a support having thereon an image-recording layer comprising a cross-linkable polymer of gelatin or acetoacetylated poly(vinyl alcohol) and a mordant;
b) applying liquid ink droplets of a cationic, water-soluble dye on the image-recording layer in an image-wise manner; and
c) applying an aqueous solution of an organic hardener or a sulfate of a trivalent metal to the image to cross-link the polymer. It was found that when an aqueous solution containing a hardener is applied to a cationic dye-based ink image where the image-receiving layer has a cross-linkable polymer and a mordant, that the wet abrasion resistance of the image is improved.
This process offers an advantage over incorporating a hardener in an ink since the hardener can be applied in both imaged and non-imaged areas, and the laydown can be precisely controlled independent of ink laydown.
The hardeners employed in the invention may be used at concentrations ranging from 0.10 to 5.0 weight percent of active ingredient in the aqueous solution, preferably 0.25 to 2.0 weight percent. This aqueous hardener solution may be applied from a ink jet print head so that the final coverage of the hardener is from about 0.00002 g/m2 to about 0.001 g/m2, preferably from about 0.00005 g/m2 to about 0.0004 g/m2.
The aqueous hardener solution may also contain, if desired, co-solvents, humectants, surfactants, and other ingredients commonly added to ink jet inks.
The organic hardener or a sulfate of a trivalent metal that can be employed in the invention include the following (including mixtures thereof):
a) formaldehyde and compounds that contain two or more aldehyde functional groups such as the homologous series of dialdehydes ranging from glyoxal to adipaldehyde including succinaldehyde and glutaraldehyde; diglycolaldehyde; aromatic dialdehydes, etc.;
b) blocked hardeners (substances usually derived from the active hardener that release the active compound under appropriate conditions) such as substances that contain blocked aldehyde functional groups, such as tetrahydro4-hydroxy-5-methyl-2(1H)-pyrimidinone polymers, polymers of the type having a glyoxal polyol reaction product consisting of 1 anhydroglucose unit: 2 glyoxal units, dimethoxylethanal-melamine non-formaldehyde resins, 2,3-dihydroxy-1,4-dioxane, blocked dialdehydes and N-methylol compounds obtained from the condensation of formaldehyde with various aliphatic or cyclic amides, ureas, and nitrogen heterocycles;
c) active olefinic compounds having two or more olefinic bonds, especially unsubstituted vinyl groups, activated by adjacent electron withdrawing groups, such as divinyl ketone; resorcinol bis(vinylsulfonate); 4,6-bis(vinylsulfonyl)-m-xylene; bis(vinylsulfonylalkyl) ethers and amines; 1,3,5-tris(vinylsulfonyl) hexahydro-s-triazine; diacrylamide; 1,3-bis(acryloyl)urea; N,N""-bismaleimides; bisisomaleimides; bis(2-acetoxyethyl) ketone; 1,3,5-triacryloylhexahydro-s-triazine; and blocked active olefins of the type bis(2-acetoxyethyl) ketone and 3,8-dioxodecane- 1, 10-bis(pyridinium perchlorate) bis(vinyl sulfonylmethane), bis(vinyl sulfonylmethyl ether), and the like; and
d) sulfates of a trivalent metal such as aluminum sulfate, iron sulfate, boron sulfate, gallium sulfate, indium sulfate, titanium sulfate, etc.
Specific examples of hardeners useful in the composition of the invention include the following:
In a preferred embodiment, the hardener employed in the composition of the invention is aluminum sulfate, bis(vinyl sulfonylmethyl ether), glutaraldehyde, 2,3-dihydroxy- 1,4-dioxane or phthaldehyde.
The aqueous hardener solution may be applied to the ink jet image in accordance with the invention in a non-imagewise manner either through a separate thermal or piezoelectric printhead, or by any other method which would apply the hardener solution evenly to the image, such as a spray bar or immersing the element in a bath of hardener. Methods of applying a hardener solution are disclosed in commonly-owned U.S. patent application Ser. No. 09/083,673 filed May 22, 1998, entitled xe2x80x9cPrinting Apparatus With Spray Bar For Improved Durabilityxe2x80x9d of Wen et al. and U.S. patent application Ser. No. 09/083,876, filed May 22, 1998, entitled xe2x80x9cInk Jet Printing Apparatus With Print Head For Improved Image Qualityxe2x80x9d of Wen et al., the disclosures of which are incorporated herein by reference.
Any cationic, water-soluble dye may be used in the invention, e.g., a dye having a positive charge obtained either by the protonation of an amino group in the dye molecule or by incorporating a positive charge into the dye chromophore. For the protonation, any acid may be used such as lactic acid, citric acid, phthalic acid, maleic acid, acetic acid, etc.
The protonated dye may be pre-formed or prepared in situ. In general, cationic dyes are basic dyes such as azo dyes, triphenylmethane dyes, azine dyes, oxazine dyes, thiazine dyes and the like having amine salt residues or quaternary ammonium groups. Specific examples of basic dyes which can be used in the invention include the following COLOR INDEX numbers: C.I. Basic Yellows 1, 2, 11, 13, 14, 19, 21, 25, 28, 32, 33, 34, 35 and 36, for yellow dyes; C.I. Basic Reds 1, 2, 9,12,13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 38, 39 and 40, and C.I. Basic Violets 7, 10, 15, 21, 25, 26, 27 and 28, for magenta dyes; C.I. Basic Blues 1,3, 5, 7, 9, 19, 21,22, 24, 25, 26, 28, 29, 40, 41, 44, 45, 47, 54, 58, 59, 60, 64, 65, 66, 67, 68 and 75, for cyan dyes; and C.I. Basic Blacks 2 and 8, for black dyes. Mixtures of these dyes may also be used.
The dye may be present in an amount of from about 0.1 to about 10% by weight, preferably from about 0.25 to about 3% by weight.
A mordant can be used in the image-recording element used in the invention to fix the cationic dye. For example, there may be used an anionic polymer such as sulfonated and carboxylated polyesters, sulfonated and carboxylated acrylates, poly(vinyl sulfonic acid), poly(vinyl styrene sulfonate sodium salt), sulfonated and carboxylated polyurethanes, sulfonated polyamides, polyolefinic emulsions, carboxylated butadiene, or derivitized anionic gelatin. In a preferred embodiment, the following mordants may be employed in a recording element used in the invention:
The above mordants may be employed in any amount effective for the intended purpose. In general, good results are obtained when the mordant is present in an amount of from about 0.5 to about 5 g/m2 of element.
As noted above, the cross-linkable polymer employed in the invention is gelatin or acetoacetylated poly(vinyl alcohol). Gelatin which may be used include the conventional lime-processed ossein, acid-processed ossein or pig skin gelatin. In addition, there are a variety of chemically-modified gelatins formed by reacting the amino group of lysine which can be used. Some functional groups that have been added to gelatin include: phthalate, phenylcarbamyl, succinyl, carbamyl, lauryl, and dodecenyl succinyl. There can also be used quaternized gel, silanol modified gel, and graft copolymers of gel with poly(styrene sulfonate), poly(vinylpyrrolidone), and poly(methacrylic acid).
The acetoacetylated poly(vinyl alcohol) useful in the invention is described in U.S. Pat. No. 4,350, 788, the disclosure of which is hereby incorporated by reference. These materials are available commercially as Gohsefimer(copyright) Z-200 from Nippon Gohsei.
The image-recording layer used in the process of the present invention can also contain various known additives, including matting agents such as titanium dioxide, zinc oxide, silica and polymeric beads such as crosslinked poly(methyl methacrylate) or polystyrene beads for the purposes of contributing to the non-blocking characteristics and to control the smudge resistance thereof; surfactants such as non-ionic, hydrocarbon or fluorocarbon surfactants or cationic surfactants, such as quaternary ammonium salts; fluorescent dyes; pH controllers; anti-foaming agents; lubricants; preservatives; viscosity modifiers; dye-fixing agents; waterproofing agents; dispersing agents; UV- absorbing agents; mildew-proofing agents; mordants; antistatic agents, anti-oxidants, optical brighteners, and the like. A hardener may also be added to the ink-receiving layer if desired.
Ink jet inks used in the process of the present invention are well-known in the art. The ink compositions used in ink jet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes, humectants, organic solvents, detergents, thickeners, preservatives, conductivity enhancing agents, anti-kogation agents, drying agents, defoamers, etc. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols.
A carrier can be present in the ink jet ink and can vary widely, depending on the nature of the ink jet printer for which the inks are intended. For printers which use aqueous inks, water, or a mixture of water with miscible organic co-solvents, is the preferred carrier medium. Co-solvents (0-20 wt. % of the ink) are added to help prevent the ink from drying out or crusting in the orifices of the printhead or to help the ink penetrate the receiving substrate. Preferred co-solvents for the inks employed in the present invention include glycerol, ethylene glycol, propylene glycol, 2-methyl-2,4-pentanediol, and diethylene glycol, and mixtures thereof, at overall concentrations ranging from 5 to 20 wt. % of the ink.
The support for the ink jet recording element used in the invention can be any of those usually used for ink jet receivers, such as paper, resin-coated paper, poly(ethylene terephthalate), poly(ethylene naphthalate) and microporous materials such as poly polyethylene polymer-containing material sold by PPG Industries, Inc., Pittsburgh, Pa. under the trade name of Teslin(copyright), Tyvek(copyright) synthetic paper (DuPont Corp.), and OPPalyte(copyright) films (Mobil Chemical Co.) and other composite films listed in U.S. Pat. No. 5,244,861.
The support used in the invention may have a thickness of from about 50 to about 500 xcexcm, preferably from about 75 to 300 xcexcm. Antioxidants, antistatic agents, plasticizers and other known additives may be incorporated into the support, if desired. In a preferred embodiment, paper is employed.
In order to improve the adhesion of the image-recording layer to the support, the surface of the support may be subjected to a corona-discharge-treatment prior to applying the image-recording layer.
In addition, a subbing layer, such as a layer formed from a halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl acetate copolymer can be applied to the surface of the support to increase adhesion of the image recording layer. If a subbing layer is used, it should have a thickness (i.e., a dry coat thickness) of less than about 2 xcexcm.
The image-recording layer may be present in any amount which is effective for the intended purpose. In general, good results are obtained when it is present in an amount of from about 5 to about 30 g/m2, preferably from about 8 to about 15 g/m2, which corresponds to a dry thickness of about 5 to about 30 xcexcm, preferably about 8 to about 15 xcexcm.